You specify deployment groups with the deploymentGroups property. It is an object whose keys are paths to deployment groups, and values contain configuration for the corresponding deployment group.
Here's an example of deployment configuration with five deployment groups:
The deployment groups in this example form the following hierarchy:
There is one root-level deployment group named all, and under it, there are deployment groups all/shared and all/application. The all/application deployment group has two children: all/application/dev and all/application/prod.